This invention relates to the art of preparing a lower alcohol ester from a soybean oil product. This purified lower alkyl soyate product has many uses, ranging from the use as a biodegradable solvent to a diesel fuel additive.
Since the end of World War II, soybeans have become a major agricultural commodity in the United States and in many other parts of the world. They are a major source of food and animal feed products for a world growing in population and, on the average, getting fed better. Each metric ton of soybeans typically contains around 183 kg of oil and around 800 kg of meal.
"Oilseeds: World Markets and Trade" in its March 1998 issue of the United States Department of Agriculture, Foreign Agricultural Service Circular Series shows that soybean production increased from 117.83 million metric tons in 1993/1994 to a projected 152.26 million tons for 1997/1998; soybean meal increased from 81.28 million metric tons in 1993/1994 to a projected 97.83 million tons for 1997/1998 and that soybean oil production from rose 18.25 million metric tons in 1993/1994 to 22.25 million tons for 1997/1998. With respect to the United States, The Wall Street Journal of Apr. 1, 1998 reported that planting in the U.S. is projected at 72 million acres as compared to a little over 60 million acres in 1995.
While the food and feed uses of soybean and its products consume by far the largest part of soybean production, industrial uses are significant and growing. While the percentage is small, it represents in actual terms significant commercial value. A recent (1997) publication, "Lipid Technologies and Applications", edited by Frank D. Gunstone et al., discusses non-food uses for soybeans, i.e., industrial uses, in chapters discussing detergents, as well as the use of oils and fatty acids in paints and surface coatings, lubricants and biofuels. Another publication (1995), "Practical Handbook of Soybean Processing and Utilization", edited by David R. Erickson, also discusses industrial uses emphasizing imminent growth of soybean usage in fuel additives, plastics and construction materials in a comprehensive chapter, "Industrial Uses for Soybeans" presented by Lawrence A. Johnson et al.
Alkyl esters from soybean oils are an important and growing part of the industrial applications of soybean products. Early uses of methylesters of soybean oil date back to the early 1940s and include uses as solvents and cleaning agents.
The prior art dating back to as early as the early 1940s consists of many techniques which discuss the alcoholysis of vegetable oils including soybean oils in the presence of a catalyst of either an acidic or caustic nature.
U.S. Pat. No. 2,271,619 describes a process to convert any higher fatty acid glyceride into lower alkyl esters by adding a saturated aliphatic monohydric alcohol with less than five carbon atoms in the presence of an alkali metal hydroxide of substantial anhydrous quality as a catalyst. The process is a batch process with the reactor temperature in the range from 86 to 212.degree. F. The quantity of monohydric alcohol is not more than 1.75 equivalents of the glyceride. The catalyst quantity is 0.1 to 0.5% by weight based upon the glyceride.
Other U.S. patents improve or add-on to the process discussed above. U.S. Pat. Nos. 2,360,844; 2,383,632; 2,383,580; 2,383,581; 2,383,614; 2,383,633; 2,383,596; 2,383,599 add variations to U.S. Pat. No. 2,271,619, respectively, a) by adding acid to the process and spray drying a phase; b) by adding the step of distilling off the unreacted alcohol; c) by controlling the influence of the catalyst--one manner suggested is by adjusting pH in the range from 5 to 7; d) by applying the technology to fatty acid partial esters; e) by volatilizing the unreacted alcohol and acidifying the liquid body for better separation of esters and glycerin; f) by reworking the partially reacted glycerides by various methods; g) by adding, in addition to an aliphatic monohydric alcohol (not methyl alcohol), a dose of methyl alcohol to improve the separation of the liquid phases; and h) by adding a solvent to aid in phase separation.
Other U.S. patents propose additional novelties and improvements. U.S. Pat. Nos. 2,494,366; 2,383,601; 3,963,699; 4,303,590; 4,371,470; 4,668,439; 5,399,731; 5,434,279; and 5,525,126 are also variations, more or less, to U.S. Pat. No. 2,271,619 respectively, a) by adding a sufficient amount of acid catalyst to the alkaline catalyst; b) by again adding an acid esterification catalyst; c) by operating the process at elevated temperatures and vacuum to ambient pressure conditions; d) by adding a second alkaline catalyzed esterification step to a first one; e) again, by adding a second esterification step is and removing the lower alkyl ester by means of an adsorbent; f) by introducing the alcohol in the form of a gas; g) by letting the reaction take place at lower temperatures and by adding an acid; g) presenting an improved method for phase separation by using an acid; and h) using a catalyst which is a mixture of calcium acetate and barium acetate.